1. Field of the Invention
The invention is related to the field of magnetic recording disk drive systems and, in particular, to burnishing a recording head to reduce the topography of the recording head.
2. Statement of the Problem
Magnetic hard disk drive systems typically include a magnetic disk, a recording head having write and read elements, a suspension arm, and an actuator arm. As the magnetic recording media is rotated, air adjacent to the disk surface moves with the disk. This allows the recording head (also referred to as a slider) to fly on an extremely thin cushion of air, generally referred to as an air bearing. When the recording head flies on the air bearing, the actuator arm swings the suspension arm to place the recording head over selected circular tracks on the rotating magnetic recording media where signal fields are written to and read by the write and read elements, respectively. The write and read elements are connected to processing circuitry that operates according to a computer program to implement write and read functions.
Recording head flying height is one of the key elements of the density of magnetic recording drives. The closer a recording head flies above the magnetic recording media, the higher density recording that can be utilized. Typically, the recording head and the recording media are each covered with a layer of overcoat material, such as carbon. The thickness of the carbon overcoat region on the head is presently approximately 2 nm, and the thickness of the media overcoat layer is presently approximately 3.8 nm to 4 nm. On top of the disk overcoat layers is a layer of lubricant material, typically 1 nm in thickness. These layers are typically deposited with an uneven topography. Thus, the media and recording head roughness limit how close the recording head can safely fly over the disk with an adequate clearance margin. Further, because of differences in lapping rates during manufacturing, the read sensor is typically recessed from the air-bearing surface (ABS), further increasing the magnetic spacing between the read sensor and the magnetic recording media.
One technique utilized to reduce the recording head roughness and recording head overcoat is to burnish the recording head surface in the region around the read sensor and the write pole in a controlled manner to remove a few nanometers of material, as described in “A novel wear-in-pad approach to minimizing spacing at the head/disk interface”, Singh, G. P.; Knigge, B. E.; Payne, R.; Run-Han Wang; Mate, C. M.; Arnett, P. C.; Davis, C.; Nayak, V.; Xiao Wu; Schouterden, K.; Baumgart, P., IEEE Transactions on Magnetics, Volume 40, Issue 4, Part 2, July 2004 Page(s): 3148-3152. The material removed typically comprises the carbon overcoat region of the recording head. Burnishing may be performed in-situ in the magnetic recording disk drive using a burnishing pad fabricated on the magnetic recording media. The recording head is burnished against the burnishing pad in a special process after the assembly of the drive until the recording head can safely clear the surface of the magnetic recording media. However, if the burnishing process proceeds into the read sensor material, then the read back signal is degraded due to thermal and mechanical stress imposed on the read sensor by the burnishing process. Thus, it is a problem for accurately determining when to stop the burnishing process such that wear does not proceed into the read sensor material.